Selective Serotonin Reuptake Inhibitors (SSRIs): A Complete Guide

Daniel Lieberman

Reviewed by Daniel Z. Lieberman, MD

Written by Nicholas Gibson

Published 06/20/2020

Updated 11/16/2023

It seems as though there’s a medication for every type of ailment. You reach for ibuprofen when you have a headache or antihistamines for allergies.

The same goes for mental health conditions like generalized anxiety disorder (also known as GAD or just anxiety) and depression (or major depressive disorder). Drugs known as antidepressants are often the first choice prescribed by healthcare professionals. And one of the most common types of antidepressants is SSRIs.

But what are SSRIs? While the world of antidepressant medications is vast, complicated and sometimes stigmatized, we’re here to uncomplicate and destigmatize things.

Keep reading to learn how SSRI drugs work, the different types of SSRIs, the side effects of SSRI drugs and more.

To understand how SSRIs work, let’s back up a minute. First, what is an SSRI drug, and what does SSRI stand for?

SSRI is short for selective serotonin reuptake inhibitor, a type of antidepressant medication.

Other antidepressants include monoamine oxidase inhibitors (MAOIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), atypical antidepressants and tricyclic antidepressants (TCAs).

Lots of acronyms, we know. But don’t worry — we’re just focusing on SSRIs.

How selective serotonin reuptake inhibitors work is sort of what their name implies. The exact mechanism is unclear, but they’re thought to increase serotonin levels by inhibiting or stopping your brain from retaking and reabsorbing serotonin, an important neurotransmitter.

Neurotransmitters like serotonin act as chemical messengers that carry signals between brain nerve cells (or neurons) and affect several bodily functions.

Serotonin, for example, affects not only mood but also sleep and digestion, among other things. Low serotonin levels are also associated with major depressive disorder (MDD).

Since SSRI drugs can affect your serotonin levels and, theoretically, improve your mood, they’re often prescribed for anxiety, depression and so many more mental health conditions, as well as other health conditions.

Currently, SSRI medications are approved by the U.S. Food and Drug Administration (FDA) for:

SSRIs may be used off-label for other conditions like eating disorders, body dysmorphic disorder and premature ejaculation, to name a few. Also, different types of SSRIs have different FDA approvals for which conditions they treat.

Not to confuse you more — that’s the opposite of what we’re here to do! — but there are different ways of naming SSRIs.

Sold under both brand names and generic labels, some of the most commonly prescribed selective serotonin reuptake inhibitors include:

While the above SSRI meds all work to increase serotonin levels, there are some differences between them.

Some research indicates that escitalopram is more effective than paroxetine and sertraline. Meanwhile, fluoxetine has a high potential for drug interactions but fewer withdrawal symptoms than other SSRIs.

Paroxetine also has a higher risk of drug interactions and may impact sleep quality more than other SSRI drugs.

Some people may not respond well to SSRIs, either because of the side effects they experience or if their depression or anxiety doesn’t improve. In that case, a healthcare professional might recommend another one of the common antidepressants.

If you’re interested in learning more about antidepressant medications, explore the above guides or read through our full list of antidepressants, which covers more than just SSRIs.

Compared to other types of antidepressants, SSRIs generally have fewer side effects while maintaining their effectiveness. In fact, since SSRIs are typically better tolerated with a lower risk of side effects, some studies have shown that fewer patients discontinue SSRI therapy than with alternative antidepressants. 

That said, SSRIs aren’t completely without side effects. We’ll go over the common side effects of SSRI drugs below, as well as rarer, more serious side effects you may encounter.

Sexual Side Effects

Sexual dysfunction is a common side effect among SSRIs. Women may experience sexual side effects such as difficulty experiencing an orgasm and decreased sex drive.

These side effects can affect both men and women. For men, adverse effects can be having difficulty  experiencing orgasm, erectile dysfunction and decreased sex drive.

Between 40 and 65 percent of people who take an SSRI experience some form of sexual dysfunction, according to a review of studies published in the journal The Mental Health Clinician.

Many SSRIs can cause sexual side effects, so the chance of experiencing adverse effects of sertraline (Zoloft) may be similar to experiencing Prozac’s sexual side effects.

However, the above review found that, of the most common SSRIs, sertraline side effects were the least likely to include sexual dysfunction.

Gastrointestinal Issues

One of the common SSRI side effects is trouble with digestion or your stomach. Gastrointestinal issues are the most commonly experienced side effects of SSRIs.

These issues can include nausea, diarrhea, constipation, vomiting and abdominal pain.


Sleep disturbances can accompany SSRI use, resulting in drowsiness or insomnia, a condition marked by difficulty falling or staying asleep.

A 2017 review of research published in the journal Current Psychiatry Reports noted that it’s common for antidepressants to affect sleep, regardless of the type. So experiencing sleep issues while taking sertraline is just as possible as Lexapro and sleep disturbance.

Weight Changes

Another potential downside of SSRI antidepressant use? Weight changes, particularly weight gain. You may have heard a rumor that Prozac causes weight gain or wonder if there’s a connection between antidepressants and weight loss.

Though some people experience weight loss when first starting an SSRI, many gain it back (and potentially more weight beyond that) after several months of treatment.

Compared to other antidepressants, SSRIs may result in less weight gain. For example, a 2011 study published in the International Journal of Neuropsychopharmacology found that those who took escitalopram (Lexapro) gained less than a third of a pound over three months compared to those who took nortriptyline, a tricyclic antidepressant.

The nortriptyline group experienced moderate weight gain.

However, antidepressants don’t affect everyone equally, so there could still be a link between Lexapro and weight changes or other SSRIs.

Dry Mouth

While not a severe or life-threatening side effect, having a dry mouth (also called xerostomia) as a result of antidepressants can be frustrating to deal with.

Dry mouth should go away on its own over several weeks, but you can also reduce the severity by avoiding caffeine, alcohol, tobacco, spicy foods and other foods and drinks that can cause dehydration.

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Nervousness, Restlessness and Agitation

If you already struggle with nervousness as a result of generalized anxiety disorder, it may be disheartening to learn that an SSRI could come with a side effect of more anxiety and worries.

While another common side effect of SSRIs is nervousness and increased agitation, it’s generally mild and resolves within about three weeks. After the initial side effect wears off, SSRIs effectively reduce anxiety.

Dizziness, Tremors and Headaches

It’s also common to experience dizziness or headaches when starting a new SSRI antidepressant, although the exact reason is unclear. Like many of the other common side effects, shaking, dizziness or headaches go away within a few weeks.

If you’re experiencing more headaches than usual while taking an SSRI, you may be tempted to reach for a painkiller to treat it. However, some painkillers can interact with SSRIs, which we’ll talk about more below.

We’ve covered almost everything you need to know about SSRIs. But there’s still some crucial information to go over.

  • Drug interactions. As mentioned above, some SSRIs can have negative interactions with other drugs, as well as supplements and even herbs. This includes monoamine oxidase inhibitors (MAOIs), St. John’s wort and other medications that increase serotonin. It’s always a good idea to inform your healthcare provider about any other medications or supplements you’re taking before starting an SSRI.

  • Serotonin syndrome. While there’s a connection between low serotonin and depression, too much serotonin in your body can be a bad thing. Another risk of taking SSRIs is serotonin syndrome, a life-threatening condition of increased serotonin levels with mild to severe symptoms. A typical SSRI dosage alone won’t cause serotonin syndrome, but taking this type of antidepressant with other medications that increase serotonin levels can.

  • SSRIs and pregnancy. While SSRIs are the most commonly prescribed antidepressants during pregnancy, they’re not without risks. Some SSRIs may harm your baby if you take them during pregnancy — however, research is conflicting. If you’re currently pregnant, breastfeeding or planning to become pregnant, discuss mental health treatment with your healthcare provider.

  • FDA black box warning: suicide risk. Like other antidepressant medications, SSRIs have a black box warning from the FDA. It notifies people of an increased risk of suicidal thoughts and/or behaviors in adolescents and young adults, primarily during the first few months of treatment. This label isn’t meant to scare you, but it’s the most serious type of FDA warning designed to provide important safety information about sertraline. The risk of this side effect is very low, and is outweighed by the risk of suicide caused by untreated depression. The black box warning shouldn’t prevent you from getting effective treatment. Instead, it should act as a signal to watch out for any emergent thoughts of suicide during the first few weeks of treatment.

  • Stopping SSRI medication. Though there may be times you want to stop taking your medication, abruptly stopping SSRI treatment can result in antidepressant discontinuation syndrome, with symptoms like insomnia, mood disturbances and flu-like symptoms. If you want to stop taking an SSRI, your healthcare provider will discuss solutions, such as a taper schedule to avoid discontinuation syndrome.

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One of the most commonly prescribed antidepressants, SSRIs are often used as a first line of treatment for several mental health conditions.

  • What are SSRIs and what does SSRI stand for? SSRIs are a group of antidepressants known as selective serotonin reuptake inhibitors that work to prevent the brain from reabsorbing serotonin, a key neurotransmitter.

  • Serotonin levels can affect your mood (among other functions) and are believed to be connected to mental health conditions, such as depression and anxiety — SSRIs are FDA-approved to treat both depression and anxiety, along with panic disorder, OCD and certain eating disorders.

  • Although they generally have fewer side effects than other antidepressants, there are still several common side effects of SSRIs. SSRI side effects include nausea, dry mouth, upset stomach, sexual dysfunction, insomnia and weight gain or loss.

While this type of medication is a common treatment option, SSRIs may not be for everyone simply because everyone’s mental health journey is different.

See our guides on SSRI alternatives as well as how to know which antidepressant is best for you when considering options.

You can also learn how to get antidepressants if you’re interested in starting an SSRI. Or you can connect with a licensed healthcare provider to discuss your symptoms and find the best treatment plan with online psychiatry.

SSRIs and antidepressants aren’t the only treatment options, of course. Talk therapy, whether in-person or through online therapy, is another helpful treatment for depression and anxiety.

Getting started with therapy is super simple, thanks to our online mental health services.

15 Sources

Hims & Hers has strict sourcing guidelines to ensure our content is accurate and current. We rely on peer-reviewed studies, academic research institutions, and medical associations. We strive to use primary sources and refrain from using tertiary references.

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This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards here.

Daniel Z. Lieberman, MD

Dr. Daniel Z. Lieberman is the senior vice president of mental health at Hims & Hers and of psychiatry and behavioral sciences at George Washington University. Prior to joining Hims & Hers, Dr. Lieberman spent over 25 years as a full time academic, receiving multiple awards for teaching and research. While at George Washington, he served as the chairman of the university’s Institutional Review Board and the vice chair of the Department of Psychiatry and Behavioral Sciences.

Dr. Lieberman’s has focused on , , , and to increase access to scientifically-proven treatments. He served as the principal investigator at George Washington University for dozens of FDA trials of new medications and developed online programs to help people with , , and . In recognition of his contributions to the field of psychiatry, in 2015, Dr. Lieberman was designated a distinguished fellow of the American Psychiatric Association. He is board certified in psychiatry and addiction psychiatry by the American Board of Psychiatry and Neurology.

As an expert in mental health, Dr. Lieberman has provided insight on psychiatric topics for the U.S. Department of Health and Human Services, U.S. Department of Commerce, and Office of Drug & Alcohol Policy.

Dr. Lieberman studied the Great Books at St. John’s College and attended medical school at New York University, where he also completed his psychiatry residency. He is the coauthor of the international bestseller , which has been translated into more than 20 languages and was selected as one of the “Must-Read Brain Books of 2018” by Forbes. He is also the author of . He has been on and to discuss the role of the in human behavior, , and .


  • 1992: M.D., New York University School of Medicine

  • 1985: B.A., St. John’s College, Annapolis, Maryland

Selected Appointments

  • 2022–Present: Clinical Professor, George Washington University Department of Psychiatry and Behavioral Sciences

  • 2013–2022: Vice Chair for Clinical Affairs, George Washington University Department of Psychiatry and Behavioral Sciences

  • 2010–2022: Professor, George Washington University Department of Psychiatry and Behavioral Sciences

  • 2008–2017: Chairman, George Washington University Institutional Review Board

Selected Awards & Honors

  • 2022: Distinguished Life Fellow, American Psychiatric Association

  • 2008–2020: Washingtonian Top Doctor award

  • 2005: Caron Foundation Research Award


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